1. Technical Field
The present invention pertains to a method and apparatus for mechanically and optically coupling an endoscope to a video camera, or the like. In particular, the invention is directed to eliminating fogging of adjacent optical windows in two mechanically and optically coupled devices.
2. Discussion of the Prior Art
Endoscopes have been successfully utilized in surgery for viewing body cavities and organs to permit diagnoses and surgical procedures to be performed internally without requiring open surgery or other invasive procedures. An endoscope is typically inserted through a small incision portal providing access to a body cavity. A lens at a distal end of the endoscope is positioned to receive light reflected from a site to be observed, and images of that site can be viewed remotely in conducting histological examinations and performing closed, or endoscopic, surgery. As utilized herein, the term endoscope refers generically to viewing devices for remotely observing otherwise inaccessible body cavities with minimal trauma and intrusion, and includes, but is not limited to, arthroscopes, colonoscopes, bronchoscopes, hysteroscopes, cystoscopes, sigmoidoscopes, laparoscopes and ureterscopes.
Endoscopes are sometimes supplied with an eyepiece at a proximal end thereof, and relay lenses in the endoscope typically produce an image for direct viewing through the eyepiece. However, adaption of video camera technology to endoscopy imaging has enabled the output image of an endoscope to be viewed on a video monitor via a video camera electronically connected with the video monitor and optically and mechanically coupled to the proximal end of the endoscope. Indirect or video monitor viewing of endoscopic images provides numerous benefits over direct viewing through an eyepiece, including: protection of viewer's vision when high intensity illumination passing through the endoscope reflects off bodily tissue at the site to be viewed; enhancement of an operator's comfort and freedom of movement; increased utility and efficiency of endoscopes; reduction in the time required to conduct endoscopic procedures; simultaneous viewing of endoscopic images by more than one person; and recordation and real time transmission of surgical procedures. When a video camera is utilized with an endoscope, an endoscope coupler is required to mechanically and optically couple the proximal end of the endoscope with the video camera, illustrative endoscope couplers being shown in U.S. Pat. Nos.: 4,569,333 (Bel et al); 4,611,888 (Prenovitz et al); 4,722,000 (Chatenever); 4,740,058 (Hori et al); 4,781,448 (Chatenever et al); 4,807,594 (Chatenever); 4,844,071 (Chen et al); 4,851,866 (Ciarlei et al); 4,863,304 (Bauer et al); and 4,969,450 (Chinnock et al).
One recurring problem in endoscope coupler design is poor image quality resulting from moisture, condensation or residue from dried moisture on transparent windows optically coupling various components of the assembly. More particularly, it is conventional for a complete endoscope assembly to include an extended probe referred to as the endoscope, an endoscope coupler and an image-forming device such as a video camera or optical eyepiece. The optical path through each of these elements is typically terminated by a window, flat or optically powered, and it is a recognized problem that moisture, condensation or residue tends to form on these windows resulting in the degradation of the surgeon's view of the surgical site. For example, the endoscope and coupler are typically sterilized by immersion in bactericidal solutions such as Cidex or Sporiciden and then rinsed with distilled water, usually leaving some residual moisture on the optical windows. If steps are taken to dry the windows, a residue may still remain. Further, moisture from surrounding air and surgical irrigation may condense on the window surfaces. In any case, the moisture or residue interferes with the surgeon's view of the surgical site.
There are numerous patents directed to methods and apparatus for eliminating "fogging" in an endoscope assembly. For example in the Chatenever '000 patent and in U.S. Pat. No. 4,076,018 (Heckele), fogging due to condensation is eliminated by providing resistive heating elements at various locations in the assembly. The presence of the resistive heating elements adds undesired complexity and cost. The Chatenever '594 patent discloses prevention of condensation by providing glass-to-glass contact between the proximal endoscope window and the adjacent distal window of the coupler. Such glass-to-glass contact requires relatively precise mechanical tolerances on the manufactured components and their assembly. The Bauer '304 patent discloses an attempt to eliminate condensation by flowing air through appropriate spaces in the endoscope assembly, thereby unduly complicating the overall design and increasing the cost. Similarly, in the Ciarlei et al '866 patent, a vent is disclosed for connection to a suction adapter employed to withdraw moisture, again complicating the structure of the system and requiring the surgeon to couple a source of suction to the vent whenever fogging is detected. It is also common in various endoscopic procedures to provide ample flow of irrigating liquid to flush debris from the surgical site. The application of suction to the instrument, as suggested by Ciarlei et al, would tend to cause the assembly to be filled with the irrigating liquid. The approach disclosed in the Prenovitz et al '888 patent is to provide O-rings at the interfaces between all components of the coupler, between the coupler and the endoscope, and between the coupler and the camera. The resulting structure is relatively complex and difficult to implement.
Each of the above-described patents is directed to a technique for avoiding fogging due to condensation. None of these patents addresses the issue of preventing degradation of image quality due to residue of dried moisture on the optical windows. U.S. Pat. No. 4,805,598 (Ueda), on the other hand, suggests that a viscous gel-like substance, free from moisture, can be utilized to fill the space between adjacent associated lenses of endoscope system components to prevent condensation of water on the lenses. The gel may be provided at one or more locations in the optical system but it appears that the gel is applied only during manufacture; that is, the gel is not applied during assembly of the components in the surgical operating theater. Accordingly, it is quite likely that condensation will form on the windows of adjacent components of the optical assembly.
Other patents having general relevance to the present invention, although not directly addressing the problem of fogging, are U.S. Pat. No. 4,641,912 (Goldenberg) disclosing the use of a water mass for coupling laser energy into an optical fiber waveguide of an endoscope, and U.S. Pat. No. 4,742,818 (Hughes et al) disclosing a seal located between components of the focusing mechanism of an endoscope to prevent sterilizing liquid from leaking between them during sterilization.
Until the present invention there has been no effective technique for eliminating both condensation on optical windows and moisture and/or residue of such moisture in an endoscope assembly.